A device disclosed in, for example, a patent document, Japanese Patent Laid-Open No. H09-221053 (Patent document 1) uses one actuator (i.e., a motor) to perform a lane keep control and a power steering control, in which (i) the lane keep control keeps a currently traveling lane (i.e., a travel along a current lane) for a subject vehicle based on an image captured by a forward-looking camera and a recognition of a relationship between the current lane and the subject vehicle and (ii) the power steering control generates the assist torque for assisting the steering operation by a driver.
The above-described device basically performs a drive control of the motor based on a total torque of a power steering torque required for the power steering control and a lane keep torque required for the lake keep control. However, during the lane keep control, an influence of the power steering control is suppressed by multiplying a coefficient, which is between 0 and 1, to the power steering torque, so that the subject vehicle does not easily run away (i.e., “derailed”) from the current lane.
When the driver interrupts the lane keep control (i.e., performs an intervening action or a so-called driver override), an actual position and an actual angle of the subject vehicle against a target position and a target angle that are set by the lane keep control respectively increase (i.e., have greater deviations), thereby causing a deviation cancelling toque to be generated by the lane keep control.
Further, the lane keep control has higher responsiveness in comparison to an assist control for coping with an external disturbance (i.e., either for ensuring a robustness or for providing a quick steering, in an order of 1 to 100 Hz (against a 0.1 Hz order of the assist control)).
However, a high responsiveness of the lane keep control may be disruptive to the driver, because the cancelling torque for cancelling the deviation by the driver override may counter the driver's operation of the steering wheel, thereby leaving a wrong feeling for the driver.
Further, when a system intervenes the steering operation by the driver, (e.g., when a danger-avoidance target follow control is performed by the system), high responsiveness of the target follow control may also leave a wrong feeling for the driver because the highly-responsive target follow control automatically steers the steering wheel toward a target control value of the target follow control in an abrupt manner. The target follow control may simply be designated as a follow control in the following description.